1. Field of the Invention
The present invention relates to a wavelength conversion apparatus for generating output light having a wavelength different from the wavelength of input light and outputting the generated output light, and an optical network system and an optical transmission system including such a wavelength conversion apparatus.
2. Related Background Art
A wavelength conversion apparatus can generate output light having a different wavelength (i.e., a different optical frequency) from the wavelength of input light and output the generated output light. Generally, in a wavelength conversion apparatus, the input light and pumping light are inputted to a nonlinear optical medium, to generate four-wave mixing (FWM) which is one type of non-linear optical phenomenon in the nonlinear optical medium and to generate output light having a new wavelength by the four-wave mixing and output the generated output light (see Japanese Laid-Open Patent Publication Nos. 10-133240 and 2000-081643).
The wavelength conversion apparatus can wavelength-convert WDM (Wavelength-Division Multiplexing) signals, obtained by multiplexing signal components in a plurality of channels with wavelengths different from each other, into TDM (Time-Division Multiplexing) signals which have a predetermined wavelength and which are multiplexed so as for them not to overlap each other along a time-line. As a method of wavelength-converting from WDM signals to TDM signals, for example, wavelength conversion methods disclosed in Document 1 (H. Sotobayashi et al., “40 Gbit/s photonic packet compression and decompression by supercontinuum generation”, Electronics Letters, Vol. 37, Issue, 2, pp. 110-111, January, 2001) and Document 2 (J. P. R. Lacey et al., “All-optical WDM to TDM transmultiplexer”, Electronics Letters, Vol. 30, Issue. 19, pp. 1612-1613, September, 1994) are known.
Namely, Document 1 discloses a method of converting inputted WDM signals into TDM signals by generating a supercontinuum to the inputted WDM signals, expanding spectra of channel signals so as for them to overlap each other, and thereafter slicing them by a specific filter. Also, Document 2 discloses a TDM conversion method using a phenomenon such that the waveforms of the WDM signals are copied onto CW (Continuous-Wave) light by introducing the WDM signals and the CW light with a wavelength to be converted into a device (EAM: Electro-Absorption Modulator) whose absorption coefficient decreases to the intensity of input light.
When the input light is light whose intensity is modulated, the output light obtained by the wavelength conversion is also similarly light whose intensity is modulated. This allows the wavelength conversion apparatus to be used in converting the wavelength of light signal transmitted in an optical network system and an optical transmission system, for example.